FR2959928A1 - SYSTEM FOR RETENTION OF AN ANCHORING DEVICE ON AN IMPLANTABLE PIECE - Google Patents

Abstract

This system comprises a retention housing (22) formed by a hole for receiving the anchoring member (2), and a retention portion (5) provided on the anchoring member (2). According to the invention, - the retention housing (22) is arranged in a part (4, 50) having a degree of elastic flexibility; - The retaining housing (22) has, on the side of a first axial end, a first collar (27) forming a continuous circular projection, adapted to be elastically deformed by said retention portion (5) that comprises the body d anchoring (2), and, on the side of a second axial end, a second collar (28) not likely to be deformed elastically by this retention portion (5).

Description

The present convention relates to a retention system of an anchoring member vis-à-vis an implantable part associated with this anchoring member. The invention finds particularly interesting applications in the vertebral field, for the retention of an anchoring screw with respect to a vertebral plate serving to immobilize two or three successive vertebrae with respect to each other, or for the retention of an anchor screw with respect to an intervertebral cage. Certain pathologies affecting the vertebrae or the intervertebral discs involve immobilizing two or three successive vertebrae relative to each other. This immobilization is frequently performed by means of metal plates placed on the front or side faces of the vertebral bodies, which are fixed to these vertebral bodies by screws engaged through holes that include these plates. This immobilization is also frequently performed by means of an intervertebral cage intended to be engaged between the trays of two vertebrae, fixed to these vertebrae by screws engaged through holes that it comprises. Such fastening screws have the important disadvantage of risking being unscrewed under the effect of the micromouvements and repeated stress exerted by the vertebrae on them, especially since the vertebrae bone concerned does not necessarily allow anchoring. of very good quality (case of an elderly patient) or that the dimensions of the vertebrae concerned do not allow to offer a very important anchoring surface (particularly in the case of the treatment of cervical vertebrae). To remedy this drawback, various means have been devised for retaining a screw on a plate, in particular in the form of bushings or split rings intended to be expanded by the screw, of split rings of the "circlip" type, of screwable inserts covering the head of one or more screws, or portions of the material of the plate foldable above the head of a screw. The existing systems have the disadvantage of either not ensuring a perfect retention in time of the screws with respect to the plate, or to imply an additional gesture for their implementation, for example the screwing of the aforementioned wafers, or not to allow orient the screw with respect to the plate in the most appropriate anchoring direction. The present invention aims to overcome all of these disadvantages.

The retention system it concerns comprises, in a manner known per se, - a retention housing formed by the peripheral face of the hole intended to receive the anchoring member, and - a retention portion arranged on the body of the anchoring, intended to be at the level of said retention housing once the anchor member is in place. According to the invention, the retention housing is arranged in a room having a degree of elastic flexibility; The retention housing has a first diameter at a first axial end, which is the one by which the anchoring member is intended to be introduced through this retention housing, and a second diameter, less than first diameter, at its second axial end; the retention housing has between these first and second diameters a maximum diameter greater than said first diameter and second diameters; this maximum diameter delimits, on the side of said first axial end, a first collar forming a continuous circular projection, the dimensions of which are such that this first collar is able to be deformed elastically, and, on the side of said second axial end, a second collar whose dimensions are such that this second collar is not likely to be deformed elastically by said retention portion that comprises the anchoring member; and this retention portion that comprises the anchoring member has a maximum diameter substantially identical to said maximum diameter of said retention housing and has a shape adapted to match that of this housing when the anchor member is put in place this retention portion thus being able to elastically deform said first collar and then to fit into the retention housing, bearing against said second collar, not likely to be deformed by it. The invention thus provides a retention system ensuring perfect retention of the anchoring member relative to the implantable part, and not implying, in order to achieve said elastic deformation, an additional gesture to that of the installation. of the anchoring member on the implantable part. Preferably, said piece having a degree of elastic flexibility is of a slightly elastically deformable material, whose degree of deformability is sufficient to allow, by elastic deformation, the passage of said retention portion beyond said first collar. This slightly elastically deformable material may especially be PEEK (polyetheretherketone).

If necessary depending on the material used for this part and the thickness thereof, the part could comprise, in its proximal portion, a series of notches delimiting between them elastically movable teeth in the radial direction. According to a possible embodiment of the invention, said retention housing is arranged directly in the wall of said implantable part.

Said piece having a degree of elastic flexibility is then said implantable piece itself. According to another possible embodiment of the invention, said retention housing is arranged in a circular ring and with a continuous peripheral wall, whose outer peripheral face is in the shape of a sphere segment and containing the equator of this sphere. ; a housing is arranged in said implantable part to receive the ring, this housing having a shape in a sphere segment containing the equator of this sphere, and having a diameter such that the ring is adapted to fit into itself and to be retained in him with the possibility of multidirectional movements of this ring in this housing. Said part having a degree of elastic flexibility is in this case formed by said ring. The aforesaid maximum diameter defines, on the side of said first axial end of the ring, a proximal portion of the ring whose average radial thickness is less than the average radial thickness of the distal portion of said ring, since said first diameter is greater than said first diameter. This smaller radial thickness allows said proximal portion to allow the forced passage of said retention portion of the anchor member beyond the first collar until receipt and retention of this retention portion in the housing defined by the inner peripheral face of the ring; the distal portion of the ring, meanwhile, because of its average radial thickness greater than that of the proximal portion of this ring, forms said second collar, which is rigid and thus fails the passage of said retention portion of the anchoring organ beyond him. Preferably, said retention housing and said retention portion 35 have spherical shapes.

The arrival of said retention portion in place in the housing formed by said retention housing makes it possible to orient the anchoring member with respect to the implantable part in the most appropriate anchoring direction thanks to the multidirectional mobility of this anchoring member in said housing.

Preferably, in this case, the maximum diameter mentioned above is the equator of the sphere segment defining the retention housing, and this equator is offset along the axis of the retention housing, on the side of said first end. According to one possibility, said first end of the retention housing is extended by a wall internally forming a conical inlet, this conical inlet promoting the introduction of said retention portion of the anchoring member beyond said first collar, into said retention housing. The invention will be better understood, and other features and advantages thereof will appear, with reference to the attached schematic drawing, showing, by way of non-limiting examples, two possible embodiments of the retention system that it relates. . Figure 1 is a sectional view of a ring that includes the retention system according to a first embodiment; Figure 2 is a view similar to Figure 1, after placement on a bone plate; Figures 3 to 6 are views of the ring and bone plate during four stages of placement of the ring on the plate; Figures 7 to 8 are views of the ring, the bone plate and a screw, together constituting the retention system, during two stages of the establishment of the screw; Figure 9 is a perspective view of the ring according to a first variant; Figure 10 is a sectional view through the axis of this ring; Figure 11 is a perspective view of the ring according to a second variant; Figure 12 is a sectional view through the axis of this ring; Figure 13 is a perspective view of a cage including, in a second embodiment, the retention system; Figure 14 is a side view of the cage, by its proximal side; Figure 15 is a view of the top cage, partially cut along the line XV-XV of Figure 14; Figure 16 is a sectional view of the cage along the line XVI-XVI of Figure 15, and Figure 17 is a sectional view of the cage along the line XVII-XVII of Figure 15.

For simplicity, the parts or elements that are found from one embodiment to another will be designated by the same reference numerals. Figures 7 and 8 show a system 1 for retaining an anchor screw 2 on a bone plate 3, which comprises, according to said first embodiment, a retaining ring 4, a retention portion 5 arranged on the screw 2 and a housing 6 arranged in the plate 3. The screw 2 comprises a threaded body 10 adapted to be placed in the bone of the body of a vertebra, a smooth cylindrical intermediate portion 11 and a head forming said retention portion 5. The latter has a sphere-segment shape containing the equator of this sphere.

The screw 2 also comprises a proximal cavity 12 allowing it to rotate, the shape of which is star-shaped in the embodiment shown in the drawing. The bone plate 3 is in particular a metal plate intended to be fixed, by means of several screws 2, to the vertebral bodies of two or three successive vertebrae in order to immobilize these vertebrae relative to each other. It comprises a plurality of screw receiving holes 2 and rings 4, each of which forms a housing 6. This housing 6 has a shape in a sphere segment which contains the equator of this sphere. The ring 4 is circular and has a continuous peripheral wall, and is made of a slightly elastically deformable material, especially PEEK (polyetheretherketone) or high density polyethylene. As is more particularly visible in FIGS. 1 and 2, it has an outer peripheral face 20 in the form of a segment of a first sphere containing the equator of this first sphere, and an inner peripheral face 21 in the form of a segment of a second sphere containing the equator of this second sphere. The respective diameters of the sphere generating the housing 6 and said first sphere are such that the ring 4 is fit to fit into this housing 6, as shown in FIG. 5, and to be retained in it with possibility. multidirectional movements in this housing, especially with the possibility of reversal 180 ° as shown by comparing Figures 5 and 6. The ring 4 internally delimits a housing 22 for retention of the retention portion 5 that includes the screw 2. The diameters respective of the sphere generating the retention portion 5 and said second sphere are such that the retention portion 5 is adapted to take place in an adjusted manner in the housing 22, as shown in Figure 8. The equator E2 of said second sphere is offset with respect to the equator E1 of said first sphere along the axis A of the ring 4, on the side of a first axial end 23 of the ring 4, which is that by which the screw 2 is intended to be introduced through the ring 4. The inner peripheral face 21 forms, between the equator E2 and the first end 23, a proximal portion of this face 21 and, between the equator E2 and the second axial end 24 opposite the first end 23, a distal portion of this face 21. Given the aforementioned offset equators E1 and E2, the degree of spherical reclosing of said proximal portion of the face 21 is less than the degree of spherical reclosing of the distal portion of this face 21; As a result, said proximal portion of the face 21 delimits, together with the outer peripheral face 20, one side of the equator E2, a proximal portion 25 of the ring 4 having a mean radial thickness less than the radial thickness. mean of the distal portion 26 extending on the other side of the equator E2. In other words, the wall of the ring 4 forms, on the proximal side, at said first end 23, a first collar 27 whose dimension in the radial direction relative to a plane T tangent to said second sphere and perpendicular to the equator E2, is significantly smaller than the dimension in the radial direction, with respect to this same plane T, of the second collar 28 formed, on the distal side, at the level of said second end 24, by the wall of the ring 4. On the side of said first end 23, the inner peripheral face 21 is interrupted so as to define a proximal opening 30 whose diameter is slightly smaller than the diameter of the retention portion 5. On the side of said second end 24, the inner peripheral face 21 is interrupted so as to define a distal opening 31 whose diameter is slightly greater than that of the intermediate portion 11 of the screw 2 and is significantly lower than that of the retention portion 5.

The average radial thickness of the proximal portion 25 of the ring 4 is such that this proximal portion 25 is able to allow for forced passage of the retention portion 5 during the introduction of this retention portion 5 into the housing 22, the resistance generated by this forced passage is however insufficient to prevent screwing the screw. As a result, this forced passage is achieved by simply continuing the screwing of the screw 2 after the arrival of the retention portion 5 in contact with the first collar 27. On the other hand, the mean radial thickness of the distal portion 26, likewise that the height and the thickness of the second collar 28, are sufficient for this distal portion 26 does not allow the passage of the retention portion 5 through it notwithstanding the slight degree of elastic deformation of the material constituting the ring 4. In addition, in the example shown, the ring 4 comprises a proximal conical inlet 32 facilitating the introduction of the screw 2 into the housing 22 of the ring 4. The ring may in particular have the following dimensions: - diameter of said first sphere : 10 mm; diameter of said second sphere: 7 mm; offset of the equator E2 with respect to the equator E1: 0.70 mm; - dimension of the first collar 27 in the radial direction relative to the plane T: 0.15 mm; - dimension of the second collar 28 in the radial direction relative to the plane T: 0.75 mm. In practice, as shown in FIGS. 3 to 8, a ring 4 is presented facing the housing 6 intended to receive it in a position turned 180 ° with respect to its position of use, that is to say with its end 23 facing the plate 3 (Figure 3). The deformability in the radial direction of the proximal portion 25 of the ring 4 allows a radial contraction of the ring 4 allowing the forced passage of this ring in the proximal inlet of the housing 6 (Figure 4) and the retention of this ring in this housing (Figure 5), with the possibility of multidirectional movements.

The ring 4 is then turned 180 ° to assume its use position (FIG. 6). The plate being placed in its implantation position, the screw 2 is then introduced through the ring 4 (FIG. 7) and is screwed until its retention portion 5 takes place in the housing 22 (FIG. 8). . As mentioned above, during this screwing, this retention portion 5 bears against the first collar 27 and elastically deform in the radial direction, to allow the crossing of the collar by the portion 5. Figures 9 and 10 show an alternative embodiment of the ring 4, wherein the equators of said first and second spheres are not offset relative to each other but on the contrary confused. In this case, the ring 4 has, on the side of said first axial end 23, a proximal portion 25 of height substantially smaller than the distal portion 26 located on the side of said second axial end 24; in the same way as before, the inner peripheral face 21 is interrupted so as to define, by a first collar 27, a proximal opening 30 whose diameter is slightly smaller than the diameter of the retention portion 5, while on the other side of said second end 24, the inner peripheral face 21 is interrupted so as to define, by a second collar 28, a distal opening 31 whose diameter is slightly greater than that of the intermediate portion 11 of the screw 2 and is much smaller to that of the retention portion 5. Figures 11 and 12 show another embodiment of the ring 4, wherein the equators of said first and second spheres are also merged. In this case, the ring 4 comprises, beyond the end 23 delimiting the first collar 27, a proximal prolongation wall 40, internally forming a conical inlet 41. This conical inlet 41 promotes the introduction of the retention portion 5 in the housing 22 delimited by the inner peripheral face 21. For the rest, the ring 4 is identical to that of Figures 9 and 10. Figures 13 to 15 show a second embodiment of the invention, in which the piece implantable is an intervertebral cage 50, intended to be inserted between the vertebral trays of two consecutive vertebrae. This cage 50 has a peripheral wall and a median partition 51 defining two cavities 52 intended to receive bone grafts. It is made of a slightly elastically deformable material, in particular PEEK (polyetheretherketone).

In its anterior face, the cage 50 comprises a median hole 53 and an impression for its mounting on the end of an impaction instrument, as well as four lateral holes 54 intended to receive screws (not shown but identical or very similar to the screw shown in Figures 7 and 8), these screws for anchoring the cage 50 to the bodies of the vertebrae between which this cage is inserted. As it appears in FIG. 14, the first and third holes 54 from the left of this figure are directed towards the top of the cage 50 and are intended to receive anchoring screws in the body of the overlying vertebra, while the second and fourth holes 54 are directed down the cage 50 and are intended to receive anchor screws in the body of the underlying vertebra.

Referring to Figures 16 and 17, it appears that each hole 54 forms anterior housing 22 constituting a retention housing of the retention portion 5 that comprises a screw 2. The housing 22, and therefore the retention housing that it constitutes , has a first diameter at its anterior axial end, which is the one by which the anchoring member is intended to be introduced through this retention housing, and a second diameter, less than said first diameter, at the level of its posterior axial end; the peripheral face of the hole 54 defining this housing 22 has between these first and second diameters, a maximum diameter comparable to E2 in the first embodiment, greater than said first diameter and second diameters; this maximum diameter E2 delimits, on the side of said front axial end, the first collet 27 adapted to be elastically deformed, which forms a continuous circular projection, and, on the side of said rear axial end, said second collar 28 not likely to be elastically deformed by the retention portion 5 that includes the screw 2.

As is apparent from the foregoing, the invention provides a system for retaining a screw 2 or other anchoring member, on a plate 3, or other implantable part, having the decisive advantages of ensuring perfect retention of the anchoring member relative to the implantable part, not to involve additional gesture to that of the establishment of the anchoring member on the implantable part, and to guide the organ of anchoring relative to the implantable piece in the most appropriate anchoring direction. The invention has been described above with reference to exemplary embodiments. It goes without saying that it is not limited to these embodiments but that it extends to all other embodiments covered by the appended claims.

Claims (9)

CLAIMS1 - System (1) for retaining an anchoring member (2) on an implantable part (3, 54), comprising: - a retention housing (22) formed by the peripheral face of the hole intended to receive the anchoring member (2), and - a retention portion (5) arranged on the anchoring member (2) intended to be at the level of said retention housing once the anchoring member has been put in place ; characterized in that: - the retention housing (22) is arranged in a part (4, 50) having a degree of elastic flexibility; - the retention housing (22) has a first diameter at a first axial end, which is the one by which the anchoring member (2) is intended to be introduced through the retention housing (22). and a second diameter, smaller than said first diameter, at its second axial end; the retention housing (22) has between these first and second diameters a maximum diameter (E2) greater than said first diameter and second diameters; this maximum diameter defines, on the side of said first axial end, a first collar (27) forming a continuous circular projection, the dimensions of which are such that this first collar (27) is able to be deformed elastically, and, on the side of said second axial end, a second collar (28) whose dimensions are such that the second collar is not likely to be deformed elastically by said retention portion (5) that comprises the anchoring member (2); and this retention portion (5) that comprises the anchoring member (2) has a maximum diameter substantially identical to said maximum diameter (E2) of said retention housing (22) and has a shape adapted to match that of this housing when the anchoring member (2) is put in place, this retention portion (5) thus being able to elastically deform said first collar (27) and then to take place in the retention housing (22) in an adjusted manner, by bearing against said second collar (28), not likely to be deformed by it. 2 - System (1) according to claim 1, characterized in that said piece (4, 50) having a degree of elastic flexibility is of a slightly elastically deformable material, whose degree of deformability is sufficient to allow, by elastic deformation, the passing said retention portion (5) past said first collar (27). 3 - System (1) according to claim 1 or claim 2, characterized in that the piece having a degree of elastic flexibility comprises, in its proximal portion, a series of notches delimiting between them elastically movable teeth in the radial direction . 4 - System (1) according to one of claims 1 to 3, characterized in that said retention housing (22) is arranged directly in the wall of said implantable part (50). 5 - System (1) according to one of claims 1 to 3, characterized in that - said retention housing (22) is arranged in a ring (4) circular and continuous peripheral wall, the outer peripheral face is in the shape of a sphere segment and containing the equator of this sphere; - a housing (6) is arranged in said implantable part (3) to receive the ring (4), the housing (6) having a sphere-shaped shape containing the equator of this sphere, and having a diameter such that the ring (4) is adapted to fit into place and to be retained in it with the possibility of multidirectional movements of this ring (4) in this housing (6). 6 - System (1) according to one of claims 1 to 5, characterized in that said retention housing (22) and said retention portion (5) have spherical shapes. 7 - System (1) according to claim 6, characterized in that said maximum diameter is the equator (E2) of the sphere segment defining the retention housing (22), and in that this equator (E2) is shifted according to the axis of the retention housing (22), on the side of said first end. 8 - System (1) according to one of claims 1 to 7, characterized in that said first end of the retention housing (22) is extended by a wall (40) internally forming a conical inlet (41), this conical inlet (41) promoting the introduction of said retention portion (5) of the anchoring member (2) beyond said first collar (27) into said retention housing (22). 9 - System (1) according to one of claims 1 to 8, characterized in that said part (4, 50) having a degree of elastic flexibility is PEEK (polyetheretherketone).